Application of the invention on board a cycle imposes on a transducer somewhat critical constructional and operational requirements. The transducer should present intrinsic qualities of sturdiness, simplification in the connections, high precision, and constant performance. These features have been difficult to achieve with traditional solutions.
For example, the use of transducers of a potentiometric kind is linked to intrinsic critical factors. These transducers generally comprise at least two parts that are in mutual sliding contact (these are, in the majority of cases, a mobile pin or brush that slides on a resistive race). In order to co-operate properly, these parts must be connected in a very precise way and must not be affected—which in practice is almost unavoidable—by stresses due to vibration and/or linked to the change in the direction of rotation, or be excessively sensitive to environmental factors, such as variations in the characteristics of the components with temperature or absorption of humidity. All of the aforesaid factors argue against the use of potentiometric transducers.
Transducers of an optical type (namely, of the type commonly referred to as optical “encoders”) overcome some of the above-mentioned drawbacks with potentiometric transducers. However, they are generally costly, can be sensitive to stresses, and usually require quite a high number of connections. In addition, optical sensors of the encoder type are intrinsically digital sensors, the detecting action of which is based upon the fact that the movement of rotation being sensed leads to alternately light and dark bands or segments passing in front of an optical sensor.
The purpose of the present invention is to provide a transducer of angular quantities for a cycle that is able to overcome the intrinsic drawbacks of the solutions according to the prior art.
In brief, the solution according to the invention is based upon the preferential use of a combination of Hall-effect sensors, preferably with analog-type outputs, i.e., such as to generate continuous transduction signals rather than a discrete digital signals, the output signals of which can assume only distinct values (namely, “0” and “1”).
Preferably, the invention envisages the use of a pair of mechanical Hall-effect sensors staggered with respect to one another by 90 mechanical degrees, with the magnetic parts not in contact. In this way it is possible to generate two electrical signals that are 90° out-of-phase with respect to one another in patterns, which vary according to a repetitive/periodic function, having preferably sinusoidal patterns or linear patterns.
The use of Hall-effect semiconductor sensors able to supply at output a voltage proportional to the induction is known. In particular, it is known that this type of sensor can supply at output both analog signals of a linear type and digital signals with single or double polarity.
By combining together different sensors and/or different polar magnetization pitches it is possible to combine together different sensor functions, including the functions of detection of speed of rotation, direction of rotation, and positioning.
Indeed it is precisely the above characteristics, combined to wide ranges of operation (also as regards temperature variations) and the considerable reliability that have contributed to the success of the above sensors in the automobile sector and in the sector of household appliances, above all for 30 controlling motors.
For example, from U.S. Pat. No. 5,332,965, a sensor is known which is designed to detect the angular position of an element such as a butterfly valve and which comprises a Hall-effect sensor, as well as a plurality of flux concentrators. The flux-concentrator configuration is designed to perform an action of linearization of the output characteristics of the Hall-effect sensor. The sensor is calibrated by varying the distance between the flux concentrator and the magnet. In one embodiment, the flux transducer performs a temperature compensation of the sensor, which is hermetically sealed so as not to be affected by phenomena of wear and/or vibration.
From European Patent No. EP 0 733 881, another angular-position sensor without contact is known which comprises a Hall-effect sensor set in a central position with respect to an annular magnet.
Again, from U.S. Pat. No. 6,104,187, a contactless magnetoresistive angular sensor is known which comprises two anisotropic magnetoresistance (AMR) elements rotated through 45° with respect to one another and comprised in respective resistive bridges. The sensor in question is designed to be used in a position detector associated to butterfly valves or to elements such as pedals, with particular care taken to ensure that the zero position of the sensor is temperature-stable.